A Spectroscopic and structural study of FeCoSb alloy

Fe, Co and Sb nanopowders were fruitfully prepared by electrical wire explosion method in Double distilled and de-ionized water (DDDW) media. The formation of iron, cobalt and antimony (FeCoSb) alloy nanopowder was monitored by X-ray diffraction. The x-ray diffraction pattern indicates that there are iron, cobalt and antimony peaks. Optical properties of this alloy nanoparticles were characterized by UV-Visible absorption spectra. The absorption peak position is shifted to the lower wavelengths when the current increases. That means the mean size of the nanoparticles controlled by changing the magnitude of the current. The surface morphological analysis is carried out by employing Scanning Electron Microscope (SEM). Particles with varies size were observed also from the images the some particles have uneven shapes with agglomerate and the other have spherical shape. The exploding FeCoSb alloy wire plasma parameters is study by optical emission spectroscopy. The emission spectra of the plasma have been recorded and analyzed. The plasma electron temperature (Te), was determined by Boltzmann plot, and the electron density (ne), by Stark broadening for wire with diameter 0.3 mm and current of 75A in distilled water.


Introduction
Nanoparticles have been a source of enormous attention because of their novel electrical, optical, physical, chemical and magnetic properties. There are a many of reports of physical and chemical processes for fabrication of nanoparticles one of them is by using plasma (exploding wire method) [1].
The nanoparticles have momentous possible for a wide range of applications like composite materials, catalysis, magnetic recording media, magnetic fluids, optoelectronic materials, fuel cells and sensors [2,3]. FeCoSb alloys are attracting greatly attention because their extraordinary physical, chemical, and magnetic properties. Recently, FeCoSb alloy nanoparticles have unique properties that be different from those of the bulk materials [4,5]. These novel properties are because high surface to volume ratio, morphology, small particle size and surface coating of nanoparticles. FeCoSb alloy nanoparticles have interesting application like biomedical and catalytic applications [6].
The preparation methods influence the properties of nanoscale metal such as iron particles. There are chemical and physical methods are used to produce metal and metalloid nanoparticles in the form of powders and colloids [7,8]. In the present study we report the characterization and unusual optical of Fe, Co and Sb nanoparticles prepared from the FeCoSb alloy using the exploding wire technique. Physical-chemical description has considered X-ray diffraction (XRD), UV-visible and scanning electron microscopy (SEM). Also The plasma which produced by exploding wire method characteristics were investigated based on optical emission spectroscopy (OES).

Experimental setup
In this work, FeCoSb alloy wire with diameter of 0.3 mm was exploded in Double distilled and de-ionized water (DDDW). The explosion was carried out with three values of current 50, 75 and 150 mA. The source voltage available was 35 volts. Referring to Fig.1, a reaction beaker with volume 500 mL was used as the explosion chamber as shown in Fig.1. When the first electrode (wire) touched the second electrode (plate) the wire vaporized, and convert into plasma. The material for wire and plate is the same but with reverse polarity. The exploded wire is related to the perfect geometry during the wire guide. The plates were set on the base of reaction beaker which filled with 100 ml of DDDW. The electrical circuit leftovers open until the contact is made by the wire on to the plate mechanically resulting in the wire explosion through a non linear process in very short time. The nanoparticles disperse in the DDDW solution. The wires have been exploded by bringing the alloy wire into speedy contact with the plate. The wire is exposed to several sparks and is being replaced after several contacts. The electrical explosion wire (EEW) process is very energy exhaustive since only relatively low voltages are applied, and also results in huge quantities of nanoparticles being formed from both the consumed electrodes.
The experimental parameters are summarized in Table 1.   Fig.3 illustrated the absorbance of nanofluid that prepared from alloy wire at different current. It is clearly from this figure that the optical properties depend on the amount of current. The absorption peak position is shifted to the ultraviolet region when the current increased that means the diameters of the particles decreases with the current increases.

X-ray diffraction (XRD)
The crystal structure of the FeCoSb alloy-nanoparticles dispersed in DDDW is examined with X-Ray diffraction. Fig.4 shows the XRD pattern of the alloy nanoparticles dispersed in DDDW. The XRD pattern as a 2 plot scanning from 20°-80° was recorded to determine crystallanity and structure. The peak obtained around 44.

Scanning Electron Microscopic (SEM)
Fundamental study of samples morphology was obtained using particular electron microscopy. It is possible to observe the external structures of nanoparticles using SEM, and it is performed to the characterize of the texture of the deposited metal as a thin film on substrate. From the images there are varies size are observed also from the images the some particles have irregular shapes with agglomerate and the other have spherical shape as shown in Fig.5.

Energy dispersive X-ray analysis
The elemental analysis of the alloy is investigation by Energy Dispersive X-ray spectroscopy (EDX) analysis as shown in Fig. 6. EDX measurement confirms the existence of the alloy in the film. From Fig. 6, there are many strong peaks for iron, cobalt and antimony but the strongest peak is to iron. The weak peak of Si and Ca shown in the EDX spectra correspond to the glass substrate material. The spectroscopic analysis Fig.7 shows the optical emission spectrum emitted from the Plasma produced by exploding FeCoSb alloy wire with diameter of 0.3mm and current 75A. The emission spectra of this alloy plasma have been recorded and analyzed. The plasma electron temperature (Te), was calculated by using Boltzman plot method, and the electron density (ne) was determine by Stark broadening using seven Fe I line at 516.74, 517.15, 522.71, 532.85, 537.1, 537.14 and 540.4 nm for the alloy wire. Also peaks at 217.581 and 556.812nm correspond to antimony (Sb I) and (Sb II) respectively. Small peaks at 258.326 and 345.351nm correspond to Co I and Co II respectively. These elements come from the FeCoSb alloy. Also some of ionic oxygen lines are founded in the inset figure. The T e values were deduced from reveres of best fitting line for the relation between ( ) versus upper energy level ( . From Fig.8, it can be noticed that the peak located at 540.3 nm corresponding to Fe line for iron atoms produced from the alloy molecular dissociate. The Fe I line was used to calculate the electron temperature. The T e value can be calculated using Fig.9 from reveres of best fitting line. The constants Values for the iron emission lines taken from reference [9]. The equations of fitting lines and the R 2 were shown in the figure. R 2 is the statistical coefficient indicating the quality of the linear fit. Table 2 shows the diameter of wire, the calculated electron temperature T e , electron density (n e ), plasma frequency (f p ) and Debye length (λ D ) for FeCoSb alloy plasma produced by exploding wire for 0.3 mm wire diameters and 75A current.   The 540.4 nm iron line peak shows in Fig. 8. The full width at half maximum was found by Gaussian fitting. From the measured width which depending on Stark effect and the standard line width for this line. The electrons density were calculated by the equation [8,9]: